1. Technical Field
The present invention relates to a non-volatile memory (also referred to below as PROM) that employs zener zap devices (also referred to below as ZapFuses) and to a semiconductor device thereof. The present invention particularly relates to a non-volatile memory suitable for suppressing heat generation during data writing accompanying increasing capacities, and to a semiconductor device of the same.
2. Related Art
As disclosed in for example Japanese Patent Application Laid-Open (JP-A) No. 2003-204069, in a zener zap device with a zap diode configured by forming a P-type well region in a surface layer of an N-type semiconductor layer, forming a P-type anode region and an N-type cathode region in the P-type well region, and with the P-type anode region and the N-type cathode region respectively connected through an anode electrode and a cathode electrode, the PN junction is broken down by applying a reverse bias voltage of a breakdown voltage or greater so as to short between the anode electrode and the cathode electrode and act as a resistor.
A PROM employing zener zap devices as storage units for single bits operates in a data write mode that zaps the zener zap devices for each bit, and in a read mode that reads the written data. In the read mode, a method and a circuit configuration are employed in which a current is applied to each of the zener zap devices for every bit, and the data of each bit is read to be transmitted to an operation circuit.
As disclosed in for example JP-A No. 2005-182899, it is necessary to provide the number of zener zap devices that matches the required storage capacity in the PROM.
As shown in the layout diagram of FIG. 10 and the cross-section of FIG. 11, a single zener zap device (ZapFuse) is configured including an N-type well, active regions, an N-type implant region, a P-type implant region, contacts and metal wiring lines.
The N-type active region in FIG. 11 is a region formed by performing N-type implantation (for example phosphorous ion or arsenic ion implantation) in an active region formed above the N-type well of FIG. 10. Moreover, the P-type active region in FIG. 11 (denoted “pac” in the drawings) is a region formed by performing P-type implantation (for example boron ion or BF2 ion implantation) in the active region formed above the N-type well of FIG. 10.
This zener zap device (ZapFuse) is represented by the circuit diagram of FIG. 12. As shown in FIG. 12, a zener zap device ZAPO is provided with two terminals, an anode and a cathode.
The P-type active region of FIG. 11 is the anode of FIG. 12, and the N-type active region in FIG. 11 is the cathode of FIG. 12.
FIG. 13 illustrates a PROM circuit configuration with n (n being an integer of 2 or more) cathodes of the zener zap devices as illustrated in FIG. 12 connected to a common line (node 0).
In FIG. 13, the respective cathodes of a zener zap device ZAP1 to a zener zap device ZAPn are each commonly connected to the node 0. The anodes of the zener zap device ZAP1 to the zener zap device ZAPn are each respectively connected to node 1 to node n.
FIG. 14 shows an example of a wiring layout of metal wiring lines in the PROM illustrated of the circuit diagram in FIG. 13.
Node 0 to node n in FIG. 14 respectively correspond to node 0 to node n in FIG. 13.
For PROM employing zener zap devices as storage units for single bits, various known technology is proposed relating to increasing capacities of PROM, such as disclosed in for example JP-A No. 2003-204069, to enable economical electrical writing on a small-scale and featuring high reliability after writing.
However, with such known technology relating to increasing PROM to high capacities, there is an issue that the surface area increases as the number of storage units (zener zap devices) is increased to achieve a higher capacity, and no consideration is given to the heat generation that accompanies such an increase in the number of zener zap devices.
Namely, in the configurations illustrated in FIG. 10 to FIG. 14, a large current flows due to zener breakdown during zener zap device writing. The zener zap devices accordingly generate heat, and due to the heat, metal in the wiring lines connected to the anodes and the cathodes increases in resistance. There is moreover also an issue of a deterioration in reliability of wiring lines due to electromigration and stress migration. These issues are particularly serious accompanying increasing capacities of non-volatile memory (PROM).